Data from: Reproductive success of captively bred and naturally spawned Chinook salmon colonizing newly accessible habitat

Captively reared animals can provide an immediate demographic boost in reintroduction programs but may also reduce the fitness of colonizing populations. Construction of a fish passage facility at Landsburg Diversion Dam on the Cedar River, WA, USA, provided a unique opportunity to explore this trade-off. We thoroughly sampled adult Chinook salmon (Oncorhynchus tshawytscha) at the onset of colonization (2003 – 2009), constructed a pedigree from genotypes at 10 microsatellite loci, and calculated reproductive success (RS) as the total number of returning adult offspring. Hatchery males were consistently but not significantly less productive than naturally spawned males (range in relative RS: 0.70 – 0.90), but the pattern for females varied between years. The sex ratio was heavily biased towards males, so inclusion of the hatchery males increased the risk of a genetic fitness cost with little demographic benefit. Measurements of natural selection indicated that larger salmon had higher RS than smaller fish. Fish that arrived early to the spawning grounds tended to be more productive than later fish, although in some years, RS was maximized at intermediate dates. Our results underscore the importance of natural and sexual selection in promoting adaptation during reintroductions.

人工繁育动物可为物种再引入计划（reintroduction programs）提供即时的种群增长助力，但同时也可能降低定植种群的适合度。美国华盛顿州锡达河（Cedar River）兰兹堡分流大坝（Landsburg Diversion Dam）的鱼类过坝设施（fish passage facility）建设项目，为探究这一权衡关系提供了独特的研究契机。本研究于种群定植初期（2003—2009年）对成年奇努克鲑（Oncorhynchus tshawytscha）开展系统性采样，基于10个微卫星位点（microsatellite loci）的基因型数据构建系谱（pedigree），并以返回的成年子代个体总数计算繁殖成功率（reproductive success, RS）。研究结果显示，人工繁育雄性个体的繁殖成功率始终低于自然产卵雄性，但差异未达统计学显著水平（相对繁殖成功率区间为0.70~0.90）；而雌性个体的繁殖成功率模式则存在显著年际差异。观测到的种群性比严重偏向雄性，因此纳入人工繁育雄性个体虽可获得些许种群统计学收益，却大幅提升了遗传适合度成本（genetic fitness cost）。自然选择（natural selection）效应检测结果显示，体型更大的奇努克鲑繁殖成功率高于体型较小的个体；较早抵达产卵场（spawning grounds）的个体通常繁殖效率高于晚到个体，但在部分年份中，繁殖成功率会在中等产卵日期达到峰值。本研究结果凸显了自然选择与性选择（sexual selection）在物种再引入过程中推动种群适应的重要意义。